Recombination-activating gene

Recombination-activating gene (RAG) plays a crucial role in the immune system, specifically in the development of B cells and T cells, which are essential components of the adaptive immune response. The RAG complex consists of two main proteins, RAG1 and RAG2, which are necessary for the initiation of V(D)J recombination. This process is vital for the generation of diverse antibody repertoires in B cells and diverse T-cell receptor (TCR) repertoires in T cells.

Function

The primary function of the RAG genes is to initiate V(D)J recombination, a site-specific recombination process that occurs only in developing B and T cells. This process involves the random assembly of variable (V), diversity (D), and joining (J) gene segments to generate unique sequences encoding the variable regions of antibodies and TCRs. The diversity of these receptors is a cornerstone of the adaptive immune system's ability to recognize a vast array of antigens.

RAG1 and RAG2 work together to introduce double-strand breaks (DSBs) at specific recombination signal sequences (RSS) adjacent to the V, D, and J segments. The DSBs are then repaired through a process involving the non-homologous end joining (NHEJ) pathway, leading to the ligation of the V, D, and J segments.

Clinical Significance

Mutations in the RAG1 or RAG2 genes can lead to severe immunodeficiency disorders, such as Severe Combined Immunodeficiency (SCID) and Omenn syndrome. These conditions are characterized by a lack of functional B and T cells, making individuals highly susceptible to infections. Diagnosis often involves genetic testing for mutations in the RAG genes, along with assessments of immune function.

Evolution

The RAG proteins are thought to have originated from a transposable element, a type of mobile genetic element that can change its position within the genome. This evolutionary origin is supported by the presence of a RAG1-like transposase domain within the RAG1 protein. The adaptation of this transposable element into the vertebrate genome, leading to the development of the RAG-mediated V(D)J recombination system, was a significant event in the evolution of the adaptive immune system.

See Also

• Adaptive immune system
• Antibody
• B cell
• T cell
• V(D)J recombination
• Severe Combined Immunodeficiency (SCID)
• Omenn syndrome